Wind turbulence is a well-known factor in the complex wildland fire environment. Sometimes it is the wind shear over vegetation, buildings, or terrain, and other times it’s the buoyant forces from solar surface heating or thermal plume injections from the fire itself.
For a smokejumper, parachuting from a low-flying aircraft in a remote and rugged landscape, turbulence near the ground at the atmospheric boundary layer (ABL) is of particular concern.
Scientists at the Rocky Mountain Research Station have published a study on how to better predict terrain-induced turbulence to assist smokejumper operations.
Smokejumpers are employed by the United States Department of Agriculture Forest Service and the Department of Interior Bureau of Land Management throughout the western US and Alaska. These smokejumpers use Ram-Air style parachutes, which require forward speed to maintain lift (USFS 2018). Small wind fluctuations can drastically impact parachute aerodynamics. Existing protocols to assess ABL turbulence during jump operations include the release of weighted streamers to visually assess the winds and turbulence. Numerous hard landings, serious accidents, and fatalities have been attributed to unexpected near-surface turbulence during training and operational jumps. Searching “Smokejumper Accident” on the Wildland Fire Lessons Learned Center’s website shows an average of four serious jump injuries per year between 2015–2023 in which turbulence potentially played a factor.
Wind flow over ridges can create large wake zones with increased turbulence that extend far downwind. This phenomenon likely contributed to the hard landing that resulted in a smokejumper fatality during a jump on the Eicks Fire in New Mexico in 2021 The research team used WindNinja, the high-resolution diagnostic wind model for wildland fire applications, to investigate surface winds and turbulence during the jump operation on the Eicks Fire. The findings indicate that the jump took place in the wake of a tall upwind ridge that created a large re-circulation zone with areas of turbulence.
WindNinja is routinely used by fire managers in the US and around the world and can drive operational fire spread models such as FlamMap and Prometheus. These uses take wind speed and direction predictions from WindNinja, however, the research notes that WindNinja can also generate information about the near-surface atmosphere, such as turbulence and shear. The researchers say these capabilities, to date, have not been made accessible to end users or formally assessed for accuracy by the development team. WindNinja has been evaluated in the field but not in the really rugged terrain where smokejumper operations often occur. Here, wind modeling is far more complex and challenging.
This study concluded that WindNinja’s lesser-known ability to simulate wind turbulence could be of use for assessing smokejumper operations under moderate to high wind conditions.
They also suggest that although this work focused on smoke jumping, real-time turbulence predictions from WindNinja could be useful for other near-surface firefighting aerial operations.
Predicting terrain-induced wind turbulence for smokejumper parachute operations is an open-access article in the International Journal of Wildland Fire.
